Token standards are critical in the blockchain ecosystem as they provide a framework for developers to create tokens with common functionalities. The two most prominent token standards on Ethereum are ERC-20 and ERC-721. ERC-20 tokens are fungible, meaning each token is identical and interchangeable (e.g., cryptocurrencies like USDT, DAI). On the other hand, ERC-721 tokens are non-fungible, where each token is unique and represents ownership of a singular item, often used for digital collectibles or NFTs (Non-Fungible Tokens). These standards ensure compatibility and interoperability between different projects and applications within the blockchain network.